This invention relates to systems and apparatus for the repulping of waste paper, particular waste paper delivered in bales.
Waste paper for recycling purposes is commonly received by the paper mill in bales, and these bales of waste paper always contain contaminating or tramp materials. It has been observed that both the quantity and the difficulty of the contamination have been increasing over the years.
Bale contamination generally includes everything that must be removed from the waste paper itself, to make the paper fibers reusable. The contamination includes objects which are foreign to the waste paper itself, such as junk, glass, rocks, staples, paper clips, styrofoam cups, packing and the like. The waste paper also includes contaminates which are bonded to or are an integral part of the paper product to be reclaimed. These include plastic films and coatings, sizing clays and printing inks.
The bales themselves may be as large as 6' feet by 4' by 4' and may weight up to 4,000 pounds. When bales are picked up and loaded by fork lift trucks, it is not uncommon for the forks to pick up some asphaltic mix or pavement on which the bales may be resting, and then the asphalt becomes entrained with the baled material.
The tramp or trash material which is extraneous to the paper products being reclaimed may be either heavier or lighter than the paper products themselves. Thus, the heavier material, known in the industry as "heavies" including rocks, glass, and metal parts, is often (but not always) separated in gravitational traps which form a part of the repulping apparatus. The lighter products, which may include extraneous tramp material in the form of cellulose, pieces of wood, styrofoam, as well as plastic material bonded to the desirable paper fibers, are generally dumped or carried into the repulper apparatus without specific attempts at prior removal or separation.
The repulper itself has the job of separating the reusable fibers from those rubber-like and plastic parts to which many of the fibers are attached. Such plastic contaminates are known in the trade as "stickies". As previously mentioned, very little effort has been made to remove the non-attached or non-associated lighter trash. This, too, ends up in the pulper not only contaminating the pulper and impeding its proper operation, but often becoming entrained with the paper fibers, and reduced in size so that the trash becomes part of the accepts. This is a particular problem with frangible plastic materials, such as styrofoam. While styrofoam, itself, is very light in weight, it can be hydraulically pulled into the pulper and broken into small pieces. It then appears in the paper stock as an extremely hard to remove contaminate.
In the handling of baled waste paper, the bales themselves are frequently dumped directly into the pulping apparatus or are broken up first and then dumped into the pulper. This practice presents to the pulper an extraneous load of trash material that adversely affects the consistency of the stock, after wetting, and impairs the operation of the pulper. Sometimes the bales or broken bales, are presoaked without first removing the contaminants as mentioned, and then applied to the pulper.
Drum-type pulpers have come into widespread use for the purpose of defibering and reclaiming fibers from waste paper, due to the ability of a drum-type pulper to provide a uniform retention or residency and due to its ability to break up the fiber adhesion without disintegrating or breaking up the unwanted substances, such as the plastic film and stickies mentioned above.
In some systems, broken bales are applied directly into the interior of a drum-type pulper without pre-cleaning or pre-sorting. One such system that has been so operated is the "Fiberflow" repulping system of A. Ahlstrom Osakeyhtio of Noormarkku, Finland, which uses a drum-type defibrator as shown in U.S. Pat. No. 4,687,146 issued Aug. 18, 1987 and U.S. Pat. No. 5,094,715 issued Mar. 10, 1982. As described in the latter patent, a primary difficulty has been that of the bale wires, etc., which adversely interfere with the defibration and with the operation of the pulper, including blocking of the pulp screens.
Further, most drum-type pulpers in use are of the rotating drum variety in which the cylindrical walls of the drum are rotated about an imaginary center axis, and the contained material is elevated by vanes on the drum interior wall and allowed to drop gravitationally back into a pool of such material within the drum, as maintained by a weir or a dam. Such drum pulpers include not only the previously mentioned patents, but also U.S. Pat. Nos. 4,385,997 issued May 31, 1983 and 4,382,559 issued May 10, 1983. Rotating drum pulpers require large and bulky roller systems by which they are supported and driven. They also require high power to operate since almost the entire content is lifted at one time.
Pre-sorting of the broken bales has been suggested for the purpose of removing undesirable fragments prior to pulping. Pre-sorting is generally accomplished in a wetted or water environment, such as shown by the apparatus in U.S. Pat. Nos. 4,194,986 issued Mar. 25, 1980 and 4,650,125 issued Mar. 17, 1987. Wet pre-sorting is generally undesirable, in part because off its use of water which must eventually be removed from the reject material, and in part by reason of its tendency to break up the stickies and plastic non-pulpable components so that they become more difficult to separate from the paper fiber.
A need therefore exists for a pulping system in which bales are disintegrated and then pre-sorted by air classification processes employing relatively inexpensive and efficient handling apparatus, and which remove both the heavies and the light weight fraction. There is a further need for improved lower cost drum-type pulpers which may be modularized and connected together in segments to provide for the desired defibering capacity for pre-sorted waste paper material.